Interaction of opioid growth factor (OGF) and opioid antagonist and their significance in cancer therapy

Targeting OGF/OGFR Signal to Mitigate Doxorubicin-induced Cardiotoxicity

Enkephalins are reportedly correlated with heart function. However, their regulation in the heart remains unexplored. This study revealed a substantial increase in circulating levels of opioid growth factor (OGF) (also known as methionine enkephalin) and myocardial expression levels of both OGF and its receptor (OGFR) in subjects treated with doxorubicin (Dox). Silencing OGFR through gene knockout or using adeno-associated virus serotype 9 carrying small hairpin RNA effectively alleviated Dox-induced cardiotoxicity (DIC) in mice. Conversely, OGF supplementation exacerbated DIC manifestations, which could be abolished by administration of the OGFR antagonist naltrexone (NTX). Mechanistically, the previously characterized OGF/OGFR/P21 axis was identified to facilitate DIC-related cardiomyocyte apoptosis. Additionally, OGFR was observed to dissociate STAT1 from the promoters of ferritin genes (FTH and FTL), thereby repressing their transcription and exacerbating DIC-related cardiomyocyte ferroptosis. To circumvent the compromised therapeutic effects of Dox on tumors owing to OGFR blockade, SiO2-based modifiable lipid nanoparticles were developed for heart-targeted delivery of NTX. The pretreatment of tumor-bearing mice with the assembled NTX nanodrug successfully provided cardioprotection against Dox toxicity without affecting Dox therapy in tumors. Taken together, this study provides a novel understanding of Dox cardiotoxicity and sheds light on the development of cardioprotectants for patients with tumors receiving Dox treatment.

Design, Synthesis, and Antitumor Evaluation of an Opioid Growth Factor Bioconjugate Targeting Pancreatic Ductal Adenocarcinoma

Pancreatic ductal adenocarcinoma (PDAC) presents a formidable challenge with high lethality and limited effective drug treatments. Its heightened metastatic potential further complicates the prognosis. Owing to the significant toxicity of current chemotherapeutics, compounds like [Met5]-enkephalin, known as opioid growth factor (OGF), have emerged in oncology clinical trials. OGF, an endogenous peptide interacting with the OGF receptor (OGFr), plays a crucial role in inhibiting cell proliferation across various cancer types. This in vitro study explores the potential anticancer efficacy of a newly synthesized OGF bioconjugate in synergy with the classic chemotherapeutic agent, gemcitabine (OGF-Gem). The study delves into assessing the impact of the OGF-Gem conjugate on cell proliferation inhibition, cell cycle regulation, the induction of cellular senescence, and apoptosis. Furthermore, the antimetastatic potential of the OGF-Gem conjugate was demonstrated through evaluations using blood platelets and AsPC-1 cells with a light aggregometer. In summary, this article demonstrates the cytotoxic impact of the innovative OGF-Gem conjugate on pancreatic cancer cells in both 2D and 3D models. We highlight the potential of both the OGF-Gem conjugate and OGF alone in effectively inhibiting the ex vivo pancreatic tumor cell-induced platelet aggregation (TCIPA) process, a phenomenon not observed with Gem alone. Furthermore, the confirmed hemocompatibility of OGF-Gem with platelets reinforces its promising potential. We anticipate that this conjugation strategy will open avenues for the development of potent anticancer agents.

The Opioid Growth Factor in Growth Regulation and Immune Responses in Cancer

It has become apparent that endogenous opioids act not only as neurotransmitters and neuromodulators, but have multiple functions in the body. Activation of the opioid system by opiate drugs is associated with a risk of cancer development through direct stimulation of tumor cell proliferation and through immunosuppression. In contrast, the endogenous peptide opioid [Met5]-enkephalin, now commonly referred to as Opioid Growth Factor (OGF), negatively regulates cell proliferation in a wide number of cells during development, homeostasis, and neoplasia. This action is mediated through the opioid growth factor receptor, originally designated the zeta (ζ) opioid receptor. Further, contrary to the traditional notion of opiates as immunosuppressive, endogenous OGF has been shown to possess a number of positive immunomodulatory properties and may provide a beneficial effect in cancer by augmenting the activity of cells involved in both innate and acquired immunity. Taken together, the evidence supports consideration of opioid peptides such as OGF as new strategies for cancer therapy.

In vitro and in vivo killing effects of methionine enkephalin on osteosarcoma

OBJECTIVE

This study aimed to investigate the underlying regulatory effects of methionine enkephalin (MENK) on osteosarcoma.

METHODS

The Cell Counting Kit-8 assay, clone formation, wound healing, transwell assay, and flow cytometry were performed to measure the effects of MENK on the proliferation, migration, invasion, and apoptosis of MG-63 and Saos-2 cells. Opiate growth factor receptor expression (OGFr) in cells was stably knocked down using siRNA. A tumor model was established by inoculating MG-63 cells into mice. Flow cytometry was performed to identify alterations in mice bone marrow, spleen, and tumor tissue immune cells. The phenotype of tumor-associated macrophages was determined using immunohistochemistry. After OGFr knockdown or/and treatment with MENK, Bax, Bcl-2, caspase 3, caspase 9, and PARP expression levels were characterized using qRT-PCR, western blot, and WES, respectively.

RESULTS

MENK could significantly inhibit the proliferation, invasion, and migration of MG-63 and Saos-2, arrest the cell cycle in the G0/G1 phase, upregulate Bax, caspase 3, caspase 9, and PARP expression, and downregulate Bcl-2 expression. Tumor size and weight were lower in the MENK group than those in the control group. MENK-treated mice exhibited a reduced ratio of CD11b + Gr-1 + myeloid-derived suppressor cells. MENK increased the ratio of M1-type macrophages and decreased the proportion of M2-type macrophages in tumor tissue. Furthermore, the level of TNF-α significantly increased while that of IL-10 decreased in MENK-treated mice. The effect of MENK could be partly reversed by OGFr knockdown.

CONCLUSION

MENK reduces the abundance of myeloid-derived suppressor cells, induces M1 polarization of macrophages, and exhibits an inhibitory effect on osteosarcoma.

Pan-Cancer Analysis and Validation of Opioid-Related Receptors Reveals the Immunotherapeutic Value of Toll-Like Receptor 4

Introduction

The relationship between the expression of opioid-associated receptors and cancer outcomes is complex and varies among studies.

Methods

This study focused on six opioid-related receptors (OPRM1, OPRD1, OPRK1, OPRL1, OGFR, and TLR4) and their impact on cancer patient survival. Bioinformatics analysis was conducted on 33 cancer types from The Cancer Genome Atlas database to examine their expression, clinical correlations, mechanisms in the tumor microenvironment, and potential for immunotherapy. Due to significantly lower expression of OPRM1, OPRD1, and OPRK1 compared to OGFR and TLR4, the analysis concentrated on the latter two genes.

Results

OGFR was highly expressed in 16 tumor types, while TLR4 showed low expression in 13. Validation from external samples, the Gene Expression Omnibus, and the Human Protein Atlas supported these findings. The diagnostic value of these two genes was demonstrated using the Genotype-Tissue Expression database. Univariate Cox regression models and Kaplan-Meier curves confirmed OGFR's impact on prognosis in a cancer type-specific manner, while high TLR4 expression was associated with a favorable prognosis. Analysis of the tumor microenvironment using a deconvolution algorithm linked OGFR to CD8+ T cells and TLR4 to macrophages. Single-cell datasets further validated this correlation. In 25 immune checkpoint blockade treatment cohorts, TLR4 expression showed promise as an immunotherapy efficacy predictor in non-small cell lung cancer, urothelial carcinoma, and melanoma.

Conclusion

In a pan-cancer analysis of 33 tissues, OGFR was consistently highly expressed, while TLR4 had low expression. Both genes have diagnostic and prognostic significance and are linked to immune cells in the tumor microenvironment. TLR4 has potential as an immunotherapeutic response marker.

Methionine enkephalin inhibited cervical cancer migration as well as invasion and activated CD11b+ NCR1+ NKs of tumor microenvironment

This study was to study the role of methionine enkephalin (menk) in cell invasion and migration as well as NK cells activation of tumor microenvironment in cervical cancer. The results showed that menk inhibited cervical cancer migration and invasion. In addition, we found menk affected epithelial to mesenchymal transition (EMT) related indicators, with increasing E-cadherin level, decreasing N-cadherin and vimentin level. Through in vivo mouse model, we found that menk IFNγ and NKP46 expression was upregulated in tumor tissues by menk compared with controls, while LAG3 expression was inhibited by menk, besides, there was an upregulation of CD11b+ NCR1+ NKs of tumor microenvironment in cervical cancer. Therefore, we concluded that menk inhibited cancer migration and invasion via affecting EMT related indicators and activated CD11b+ NCR1+ NKs of tumor microenvironment in cervical cancer, laying a theoretical foundation for the further clinical treatment of menk.

Precision management of post-COVID pain: An evidence and clinical-based approach

Background Pain after a SARS-CoV-2 acute infection (post-COVID pain) is becoming a new healthcare emergency but remains underestimated and most likely undertreated due to a lack of recognition of the phenomenon and knowledge of the underlying pain mechanisms. Evidence supporting any particular treatment approach for the management of post-COVID pain is lacking. Large variability in the patient response to any standard pain treatments is clinically observed, which has led to calls for a personalized, tailored approach to treating patients with chronic post-COVID pain (i.e. 'precision pain medicine'). Applying the global concerted action towards precision medicine to post-COVID pain could help guide clinical decision-making and aid in more effective treatments. Methods The current position paper discusses factors to be considered by clinicians for managing post-COVID pain ranging from identification of the pain phenotype to genetic consideration. Results The ability of clinicians to phenotype post-COVID pain into nociceptive, neuropathic, nociplastic or mixed type is suggested as the first step to better planification of a treatment programme. Further, the consideration of other factors, such as gender, comorbidities, treatments received at the acute phase of infection for onset-associated COVID-19 symptoms, factors during hospitalization or the presence of emotional disturbances should be implemented into a treatment programme. Conclusions Accordingly, considering these factors, management of post-COVID pain should include multimodal pharmacological and non-pharmacological modalities targeting emotional/cognitive aspects (i.e. psychological and/or coping strategies), central sensitization-associated mechanisms (i.e. pain neuroscience education), exercise programmes as well as lifestyle interventions (e.g. nutritional support and sleep management). SIGNIFICANCE: This position paper presents an evidence-based clinical reasoning approach for precision management of post-COVID pain.

Involvement of the Opioid Peptide Family in Cancer Progression

Peptides mediate cancer progression favoring the mitogenesis, migration, and invasion of tumor cells, promoting metastasis and anti-apoptotic mechanisms, and facilitating angiogenesis/lymphangiogenesis. Tumor cells overexpress peptide receptors, crucial targets for developing specific treatments against cancer cells using peptide receptor antagonists and promoting apoptosis in tumor cells. Opioids exert an antitumoral effect, whereas others promote tumor growth and metastasis. This review updates the findings regarding the involvement of opioid peptides (enkephalins, endorphins, and dynorphins) in cancer development. Anticancer therapeutic strategies targeting the opioid peptidergic system and the main research lines to be developed regarding the topic reviewed are suggested. There is much to investigate about opioid peptides and cancer: basic information is scarce, incomplete, or absent in many tumors. This knowledge is crucial since promising anticancer strategies could be developed alone or in combination therapies with chemotherapy/radiotherapy.

Methionine enkephalin inhibited cervical carcinoma via apoptosis promotion and reduction of myeloid derived suppressor cell infiltrated in tumor

Immunotherapy for cervical carcinoma is becoming increasingly important recently. In these studies methionine enkephalin (menk) is shown to inhibit cervical tumor cell proliferation in vitro in association with an increase in the expression of apoptosis markers and mediators, including an increase in fas, caspase 8, and caspase 3 expression and intrinsic expression of the signaling pathway mediator bax. In vivo, tumor growth was restrained in mice xenotransplant model with typical pathological features of apoptosis. Furthermore, myeloid derived suppressor cells (MDSCs) had a significant decrease in circulation and in tumor site. In brief, these findings showed menk could inhibit tumor growth in vitro and in vivo, providing direction of further research and clinical application prospect.

Antagonists of the Mu-Opioid Receptor in the Cancer Patient: Fact or Fiction?

Purpose of Review

Antagonists of mu-opioid receptor role in cancer progression remains to be elucidated. The objective of this review was to summarize the available evidence on antagonists of mu-opioid receptor effect on tumor progression and prognosis in different types of cancers and an evaluation of the available findings on their mechanism of action.

Recent Findings

We have found studies related to methylnaltrexone (MNTX) and naltrexone (NTX) usage in cancer outcomes-related setting. We found consistent preclinical evidence of a potential action of MNTX and NTX on cancer growth and spread mediated mainly by effect on the opioid growth factor receptor (OGFr) axis, which results in depressed cell replication. However, clinical results are scarce and limited to poor-quality evidence.

Summary

Further high-quality studies are warranted to study antagonists of mu-opioid receptor role as a therapeutic option in different types of cancer, especially in patients where the classical treatment causes unacceptable side effects.

Opioids and Ocular Surface Pathology; A Literature Review of New Treatments Horizons

This review discusses the role of opioids in the corneal surface and the different pathways and therapeutic methods of management. A literature review was performed using PubMed database. For the database search, the main searching words “opioid” and “topical opioid treatment” were used with the descriptors “cornea”, “ocular surface”, “neuropathic corneal pain”, “corneal sensitivity” and “naltrexone”; original scientific articles and reviews were included to achieve the purpose of the review. The endogenous opioid system has relevant functions in the organism, and in daily use, opioids are used as painkillers. However, these drugs may be employed for other indications as opioid pathways have a wide spectrum. The corneal surface for topical treatment is easily accessible, hence sparing the side effects of systemic opioids. Instillation of opioid antagonist substances, such as naltrexone, increases corneal healing rates and stimulates the division of corneal epithelium cells without deleterious effects. The natural modulation of endogenous opioids controls different forms of pain, including inflammatory and neuropathic pain, both in the ocular surface and in the central nervous system. There are diverse methods in controlling pain using opioids, especially in refractory forms. This review attempts to collect the literature about corneal surface and opioid pathways to provide an overview image and a possible direction of the news treatments.

Regulatory role of methionine enkephalin in myeloid-derived suppressor cells and macrophages in human cutaneous squamous cell carcinoma

The antitumor effects of methionine enkephalin (MENK), also known as opioid growth factor (OGF), including its inhibitory effects on cutaneous squamous cell carcinoma (CSCC), have been established. In this study, we determined the precise mechanism by which MENK suppresses CSCC cell growth. In particular, MENK induced G0/G1 cell cycle arrest and promoted apoptosis in CSCC cells via the Bcl-2/Bax/Caspase-3 signaling pathway. Moreover, MENK reduced immunosuppression by downregulating the number of myeloid-derived suppressor cells (MDSCs) and regulating the polarization of tumor-associated macrophages from M2 to M1 in vivo. Furthermore, JAK2/STAT3, an important tumor-promotion and immunosuppression signaling pathway that is involved in MDSC expansion in tumors and macrophage polarization, was inhibited. These findings highlight the potential of the JAK2/STAT3 signaling pathway as a therapeutic target and suggest the clinical application of MENK for CSCC.

Preclinical and clinical studies into the bioactivity of low-dose naltrexone (LDN) for oncotherapy

Naltrexone (NTX) is a nonspecific opioid antagonist that exerts pharmacological effects on the opioid axis by blocking opioid receptors distributed in cytoplastic and nuclear regions. NTX has been used in opioid use disorder (OUD), immune-associated diseases, alcoholism, obesity, and chronic pain for decades. However, low-dose naltrexone (LDN) also exhibits remarkable inhibition of DNA synthesis, viability, and other functions in numerous cancers and is involved in immune remodeling against tumor invasion and chemical toxicity. The potential anticancer activity of LDN is a focus of basic research. Herein, we summarize the associated studies on LDN oncotherapy to highlight the potential mechanisms and prospective clinical applications.

Successive treatment with naltrexone induces epithelial-mesenchymal transition and facilitates the malignant biological behaviors of bladder cancer cells

Naltrexone is widely used for alleviating opioid-related side effects in cancer patients. However, the effects of naltrexone on cancer progression are controversial in the literature. The present study was carried out to investigate the effects of successive treatment with clinically relevant doses of naltrexone on the malignant biological behaviors of bladder cancer cells. The human bladder cancer T24 cells and mouse bladder cancer MB49 cells were treated with naltrexone. Cell proliferation, migration, and invasion abilities were analyzed. Morphological changes of the cells were confirmed by F-actin immunofluorescence staining. Epithelial-mesenchymal transition (EMT)-related markers and transcriptional factors, as well as activation of the phosphatidylinositol 3 kinase (PI3K)/AKT signaling pathway, were analyzed. Results showed that, compared with the control group, successive treatment with naltrexone significantly promoted the proliferation and decreased the apoptosis of bladder cancer cells, together with increase in cell migration and invasion ability. Continuous treatment with naltrexone also significantly reduced the expression of epithelial markers (E-cadherin and cytokeratin 19), increased the expression of mesenchymal markers (N-cadherin and vimentin) and EMT-inducing transcription factors (Snail and Slug), and further shifted the morphological phenotype of bladder cancer cells to a mesenchymal phenotype. The PI3K/AKT signaling pathway was activated by successive treatment with naltrexone. Notably, incubation with the specific PI3K inhibitor LY294002 together with naltrexone reversed the naltrexone-induced EMT progression. In conclusion, successive treatment with naltrexone may be favorable for the progression of bladder tumors by activating the PI3K/AKT signaling pathway and inducing EMT. Long-term exposure to naltrexone should be used cautiously in patients with bladder cancer.